Embodiments of this invention generally relate to an elevator system, and more particularly, to the position reference system of an elevator system.
Modern elevator systems are generally designed to be capable of determining the current position of the elevator systems' cars. Elevator position devices are commonly used to determine current car position. However, after a power loss or hard system reset, existing elevator control systems may not retain current car position data. Furthermore, the systems may not be able to determine the current positions of their cars for various reasons. For example, shaft encoders are commonly used to monitor elevator car position. These encoders work by counting the number and direction of shaft rotations, or partial rotations, following an absolute position determination. Based on the number of rotations since determining a known position, a processor is able to determine the current location of an elevator car. However, following a power outage, the encoders generally lose the data pertaining to the number of rotations, and possibly the data identifying the last known absolute position. Without this data, the shaft encoders are unable to determine current car position without an interruption of service to perform a position recovery procedure such as a terminal position recovery run.
In a terminal position recovery run, an elevator is run in one direction (up or down) in its hoistway until an initialization switch is activated. Because initialization switches are located at distal ends of the hoistway, activation of one of the switches indicates that the car is physically located at the corresponding end of the hoistway , a known absolute position. The position monitoring system is then able to set the current car position as a known position. Once an absolute position is established, a shaft encoder or the like can be used to determine relative movement, thereby tracking the current car position. This method generally involves placing some form of sensor at each terminal landing (the upper and lowermost landings), as well as on the elevator car. In some known systems, initialization magnets and door zone magnets are placed at both the top and bottom landing.
In these known systems, when an elevator car is located between the terminal landings when car position information is lost, the elevator car must be moved to one of the terminal landings to reset the elevator position device. When the elevator car position information is lost near one of the terminal landings, such that the elevator position device detects one of the terminal magnets, the elevator controller cannot use that landing to reset the elevator position device. Accordingly, the elevator controller causes the elevator car to perform a correction run to the other end of the hoistway to reset the elevator position device. While such long correction runs ensure high performance leveling of elevator cars, they require a large amount of time to complete and are detrimental to elevator performance.